Walkers are used by people with walking difficulties to support them while walking. An exemplary walker is the Hugo Rollator™. Walkers need to be manipulable by a user, and thus need to be relatively light. Consequently, walkers tend not to be motorized. One walker, shown in U.S. Pat. No. 5,390,753, is provided with drive wheels, but the rear wheels are lifted up to cause the drive wheels to contact the ground (thus reducing stability) and the design does not include a seat. On the other hand, motorized wheelchairs, such as described in U.S. Pat. No. 6,199,647, are known that have a mid-wheel drive, but these tend to be heavy and the drive wheels are permanently engaged. There is a need for a new motorized walker.